Trimming (computer programming)

<h2 id="variants">Variants</h2>
<h3>Left or right trimming</h3>
<p>The most popular variants of the trim function strip only the beginning or end of the string. Typically named ltrim and rtrim respectively, or in the case of Python: lstrip and rstrip. C# uses TrimStart and TrimEnd, and Common Lisp string-left-trim and string-right-trim. Pascal and Java do not have these variants built-in, although <a href="/facts/Object_Pascal/cuGkuISv">Object Pascal</a> (Delphi) has TrimLeft and TrimRight functions.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a>
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<h3>Whitespace character list parameterization</h3>
<p>Many trim functions have an optional parameter to specify a list of characters to trim, instead of the default whitespace characters. For example, PHP and Python allow this optional parameter, while Pascal and Java do not. With Common Lisp's string-trim function, the parameter (called <i>character-bag</i>) is required. The C++ <a href="/facts/Boost_library/vGLGG51A">Boost library</a> defines space characters according to <a href="/facts/Locale_(computer_software)/Hwbtpj4e">locale</a>, as well as offering variants with a <a href="/facts/Predicate_(computer_programming)/5WazAvKF">predicate</a> parameter (a <a href="/facts/Functor/l2u3rIBE">functor</a>) to select which characters are trimmed.
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<h3>Special empty string return value</h3>
<p>An uncommon variant of trim returns a special result if no characters remain after the trim operation. For example, <a href="/facts/Jakarta_Project/9fB1VNS8">Apache Jakarta</a>'s StringUtils has a function called stripToNull which returns null in place of an empty string.
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<h3>Space normalization</h3>
<p>Space normalization is a related string manipulation where in addition to removing surrounding whitespace, any sequence of whitespace characters within the string is replaced with a single space. Space normalization is performed by the function named Trim() in spreadsheet applications (including <a href="/facts/Microsoft_Excel/Ezal6G75">Excel</a>, <a href="/facts/OpenOffice.org_Calc/561WcNgg">Calc</a>, <a href="/facts/Gnumeric/HXPlB5yy">Gnumeric</a>, and <a href="/facts/Google_Docs/y2RYkhAQ">Google Docs</a>), and by the normalize-space() function in <a href="/facts/XSL_Transformations/0gw4WVyJ">XSLT</a> and <a href="/facts/XPath/0eCtJoj7">XPath</a>, 
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<h3>In-place trimming</h3>
<p>While most algorithms return a new (trimmed) string, some alter the original string <a href="/facts/In-place/Ghe2PJUF">in-place</a>. Notably, the <a href="/facts/Boost_library/vGLGG51A">Boost library</a> allows either in-place trimming or a trimmed copy to be returned.
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<h2 id="definition-of-whitespace">Definition of whitespace</h2>
<p>The characters which are considered whitespace varies between programming languages and implementations. For example, C traditionally only counts space, tab, line feed, and carriage return characters, while languages which support <a href="/facts/Unicode/DDu3MfPV">Unicode</a> typically include all Unicode space characters. Some implementations also include <a href="/facts/ASCII/vGUI33Qu">ASCII</a> control codes (non-printing characters) along with whitespace characters.
</p><p>Java's trim method considers ASCII spaces and control codes as whitespace, contrasting with the Java isWhitespace() method,<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> which recognizes all Unicode space characters.
</p><p>Delphi's Trim function considers characters U+0000 (NULL) through U+0020 (SPACE) to be whitespace.
</p>
<h3>Non-space blanks</h3>
<p>The <a href="/facts/Braille_Patterns/qu7hAGNQ">Braille Patterns</a> Unicode block contains U+2800 ⠀ BRAILLE PATTERN BLANK, a <a href="/facts/Braille/SKtJVCmc">Braille</a> pattern with no dots raised. 
The Unicode standard explicitly states that it does not act as a space.
</p><p>The <a href="/facts/Non-breaking_space/lBPo5IS6">Non-breaking space</a> U+00A0   NO-BREAK SPACE (&nbsp;, &NonBreakingSpace;) can also be treated as non-space for trimming purposes.
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<h2 id="usage">Usage</h2>
<p class="note">Main article: <a href="/facts/Comparison_of_programming_languages_(string_functions)/ALwbntgo">Comparison of programming languages (string functions) § trim</a></p>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://www.tcl.tk/man/tcl8.4/TclCmd/string.htm#M46">Tcl: string trim</a></li>
<li><a href="https://blog.stevenlevithan.com/archives/faster-trim-javascript">Faster JavaScript Trim</a> - compares various JavaScript trim implementations</li>
<li><a href="http://webwidetutor.com/php/PHP-Change-String-value-behaviour-or-look-?id=8">php string cut and trimming</a>- php string cut and trimming</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Trim". Freepascal.org. 2013-02-02. Retrieved 2013-08-24. <a href="https://www.freepascal.org/docs-html/rtl/sysutils/trim.html" target="_blank">https://www.freepascal.org/docs-html/rtl/sysutils/trim.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Character (Java 2 Platform SE 5.0)". Java.sun.com. Retrieved 2013-08-24. <a href="https://java.sun.com/j2se/1.5.0/docs/api/java/lang/Character.html#isWhitespace(char)" target="_blank">https://java.sun.com/j2se/1.5.0/docs/api/java/lang/Character.html#isWhitespace(char)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Trimming (computer programming) open-in-new

Trimming (computer programming)